1. Field of the Invention
The present invention relates generally to processing signals from magnetoresistive (MR) and giant magnetoresistive (GMR) storage media heads using matched filters.
2. Description of the Related Art
In data recording devices such as magnetic disk drives and tape drives, MR and GMR heads are used to read data that has been recorded on the devices. These heads detect magnetic transitions on the storage medium that have been previously established (xe2x80x9cwrittenxe2x80x9d) on the medium to represent data. The output voltage of the head, including its phase, represents the transitions and, thus, the data on the medium.
As recognized herein, random and systematic errors can be introduced in the output signal of read heads in several ways. For example, errors can be introduced by incorrect read performance of the read head itself. To detect errors, data can be encoded with error correction symbols prior to writing and then decoded during the read process and checked to determine whether any errors occurred, but it is possible that a loss of synchronization between the encoding and decoding operations can itself result in errors. Errors can also be caused by so-called xe2x80x9cthermal asperitiesxe2x80x9d, wherein the head accidentally contacts the recording medium (or a particle that rests on the medium).
In any case, significant encoding and decoding is undertaken along with accompanying error detection and correction as part of storing and retrieving data on, e.g., hard disk drives. The present invention understands that as the density of data on storage media increases and as the data transfer rates associated with improved storage devices also increase, the process of data storage and retrieval, including error detection and correction, grows ever more complicated. Moreover, when data is read every clock period and the clock periods grow ever shorter, the energy consumed by the read circuitry grows, an undesirable outcome particularly in the context of smaller, battery-powered computing devices.
In existing MR read devices the signal from the read head is shaped by an amplitude equalizer (xe2x80x9cPR equalizerxe2x80x9d) and then sampled every clock period, with the sampled amplitudes of the shaped pulses then being digitized and their values used for detection. The present invention understands that this process, which requires sampling the output of the head each clock period, becomes performance-limiting and energy inefficient as the clock period shortens. Furthermore, the phase of the transitions sensed by the read head and represented by the output signal of the head cannot be measured directly using the PR equalizer structure, but must be indirectly determined by subsequent processing, which is undesirable as the data transfer rates of hard disk drives increase.
A read system includes a matched filter that is defined preferably by the geometric parameters of a read head device. The matched filter generates a matched output. A signal combiner combines the matched output with a read signal that represents magnetically stored data and that is generated by a read head of the read head device, and more particularly that represents the phase of an N-clock portion of a magnetic readback signal.
In a preferred embodiment, the matched output includes at least one symbol, and the matched filter generates successive symbols every N clock periods, wherein N is an integer such as three. Also, a complex correlator receives the combined signal and correlates the matched output with the read signal to render a correlated signal. In a preferred implementation, the signal combiner multiplies the matched output by the read signal to render the combined signal and the complex correlator integrates the combined signal. As disclosed in greater detail below, at the complex correlator output each symbol is represented as an imaginary number and a real number.
In a particularly preferred implementation, the matched filter includes a transform for generating the real number component of each symbol. Further, the matched filter includes delays, with each delay being characterized by a respective distance defined by the geometry of the head device. If desired, a phase equalizer can be provided for receiving the combined signal and equalizing phases between symbols, and then outputting a phase-equalized signal to the complex correlator.
In another aspect, a method for processing a signal from an MR or GMR head having a response includes generating a model of the response, and then generating a matched filter using the model. The method also includes processing an actual read signal from the head using the matched filter.
In still another aspect, a circuit is disclosed for processing a read signal from an MR or GMR read head device. The circuit includes a signal generator that generates a signal modelled on an expected signal of the read head device. A combiner receives the signal from the signal generator and combines it with the read signal to render a combined signal. Also, a phase equalizer processes the combined signal, and a correlator receives the output from the phase equalizer and generates a correlated signal.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: